Cellular communication systems provide wireless communication services in many populated areas of the world. While cellular communication systems were initially constructed to service voice communications, they are now called upon to support data communications as well. The demand for data communication services has exploded with the acceptance and widespread use of the Internet. While data communications have historically been serviced via wired connections, cellular users now demand that their wireless units also support data communications. Many wireless subscribers now expect to “surf” the Internet, access email, and perform other data communication activities using their cellular phones, wireless personal data assistants, wirelessly linked notebook computers, and/or other wireless devices. The demand for wireless communication system data communications continues to increase with time. Thus, existing wireless communication systems are currently being created or modified to service these burgeoning data communication demands.
Cellular networks include a network infrastructure that wirelessly communicates with wireless terminals within a respective service area. The network infrastructure typically includes a plurality of base stations dispersed throughout the service area, each of which supports wireless communications within a respective cell or set of sectors. The base stations may be coupled to base station controllers (BSCs), with each BSC serving a plurality of base stations. Each BSC is coupled to a mobile switching center (MSC). Each BSC also typically directly or indirectly coupled to the Internet.
In operation, each base station (BS) communicates with a plurality of wireless terminals operating in its cell/sectors. A BSC coupled to the base station routes voice communications between the MSC and the serving base station. The MSC routes the voice communication to another MSC or to the PSTN, for example. The BSCs route data communications between a servicing base station and a packet data network that may include or couple to the Internet. Transmissions from base stations to wireless terminals are referred to as “forward link or downlink” transmissions while transmissions from wireless terminals to base stations are referred to as “reverse link or uplink” transmissions.
Third generation (3G) cellular networks have been specifically designed to fulfill these future demands of the mobile Internet. As these services grow in popularity and usage, factors such as cost efficient optimization of network capacity and quality of service (QoS) will become even more essential to cellular operators than it is today. These factors may be achieved with careful network planning and operation, improvements in transmission methods, and advances in receiver techniques. To this end, carriers need technologies that will allow them to increase downlink throughput and, in turn, offer advanced QoS capabilities and speeds that rival those delivered by cable modem and/or DSL service providers. In this regard, networks based on wideband CDMA (WCDMA) technology may make the delivery of data to end users a more feasible option for today's wireless carriers.
A mobile handset may receive and/or decode signals received in a downlink channel from a base station based on coherent detection or noncoherent detection. For coherent detection, the base station may transmit a pilot channel that contains a bit pattern upon which the mobile handset may compute a channel estimate, which characterizes the wireless medium, or channel, through which signals travel between the base station and the mobile handset. The channel estimate, or channel state information (CSIT) may enable detection of information, or symbols, contained in received and/or decoded signals. In a closed loop transmit diversity system, the CSIT may be communicated to the base station in an uplink channel. For noncoherent detection, the mobile handset may attempt to decode received signals without utilizing CSIT.
The characteristics signals transmitted by the base station, for example amplitude and or phase, may be altered as the signals travel in the wireless medium and are received at the mobile terminal. The alteration of the signals may be referred to as fading. In addition to fading, the received signals may comprise noise that was introduced during the travel of the signals through the wireless medium.
The received signal may be spread and scrambled wherein the scrambled signal comprises a plurality of chips. The mobile terminal may descramble the scrambled signal and despread (integrate, or sum) the descrambled signal to detect a symbol. The number of chips contained in a detected symbol may comprise an integration length.
When the integration does not comprise a sufficiently long time interval, the noise component may not be attenuated sufficiently to achieve a desired signal to noise ratio (SNR), wherein the signal refers to the altered signal component in the received signal, and the noise refers to the noise component in the received signal. However, when the mobile terminal is in motion relative to the base station, the CSIT information may be dynamic. Thus, when the integration comprises too long of a time interval with coherent detection, the CSIT may change during the integration time interval, which may result in erroneous detection of symbols. This may also result in a failure to achieve a desired SNR for the received signals.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.